Differential scanning calorimetry study of glass transition in frozen starch gels

Analysis of cryopreservation media thermophysical characteristics after ultra-rapid cooling through differential scanning calorimetry

Cryoprotective agents play a critical role in minimizing cell damage caused by ice formation during cryopreservation. However, high concentrations of CPAs are toxic to cells and tissues. Required concentrations of CPAs can be reduced by utilizing higher cooling and warming rates, but insight into the thermophysical properties of biological solutions in the vitrification method is necessary for the development of cryopreservation protocols. Most studies on thermophysical properties under ultra-rapid cooling conditions have been qualitatively based on visualization. Differential scanning calorimetry methods are ideal for studying the behavior of biomaterials in various freezing conditions quantitatively and accurately, though previous studies have been predominantly restricted to slower cooling rates. Here, we developed an ultra-rapid cooling method for DSC that can achieve minimal cooling rates exceeding 2000 °C/min. We investigated the thermophysical vitrification behavior of ternary solutions of phosphate buffer saline (1X), dimethyl sulfoxide or glycerol and ice blocking polymers (X-1000 or Z-1000). We quantified the impact of solute concentration on ice crystal formation during rapid cooling. Our findings support the expectation that increasing the solute concentration reduces the amount of ice formation, including devitrification. Devitrification increases from 0 % to 40 % (v/v) Me2SO and then reduces significantly. The relative amounts of devitrification to the total ice formation are 0 %, 60 %, 0 % in 20 %, 40 %, 60 % (v/v) Me2SO, and 2 %, 48 %, 49 % in 20 %, 40 %, 60 % (v/v) glycerol, respectively. The results suggest that at low concentrations, such as below 20 % (v/v) for Me2SO or glycerol, increasing the warming rate after ultra-rapid freezing is not essential to eliminate devitrification. Furthermore, ice blocking polymers do not reduce ice formation substantially and cannot eliminate devitrification under ultra-rapid cooling conditions. In conclusion, our results provide insights into the impact of solute concentration on ice formation and devitrification during rapid cooling, which can be practical for optimizing cryopreservation protocols.

Tailoring 3D-printed high internal phase emulsion-rice starch gels: Role of amylose in rheology and bioactive stability

This study investigated the properties of 3D-printed high internal phase emulsion (HIPE)-rice starch gels, specially tailored for personalized nutrition by co-encapsulating resveratrol and β-carotene. We examined the influence of amylose content on various parameters, including functional groups, linear and nonlinear rheology, printed precision and microstructural stability. Additionally, we assessed the protective efficacy and release in vitro digestion of these gels on the encapsulated bioactive components. Compared to HIPE, HIPE-starch gels differently impacted by amylose content in starches. Low-level amylose weakened the network structure, attributed to amylose mainly responsible for gel formation and weak hydrogen bond interaction between the surface-active molecules and amylose due to gelatinized starch granules rupturing the protein network. Oppositely, high-level amylose led to denser, more gel-like structures with enhanced mechanical strength and reversible deformation resistance, making them suitable for 3D printing. Furthermore, 3D-printed gels with high-level amylose demonstrated well-defined structures, smooth surfaces, stable printing and less dimension deviation. They were also regarded as effective entrapping and delivery systems for resveratrol and β-carotene, protecting them against degradation from environment and damage under the erosion of digestive fluid. Overall, this research offers a straightforward strategy for creating reduced-fat HIPE gels that serve as the carrier for personalized nutraceutical foods.

Effect of Germinated Sorghum Extract on the Physical and Thermal Properties of Pre-Gelatinized Cereals, Sweet Potato and Beans Starches

Starches from different botanical sources are affected in the presence of enzymes. This study investigated the impact of α-amylase on several properties of pre-gelatinized starches derived from chickpea (Cicer arietinum L.), wheat (Triticum aestivum L.), corn (Zea mays L.), white beans (Phaseolus vulgaris), and sweet potatoes (Ipomoea batatas L.). Specifically, the water holding capacity, freezable water content, sugar content, and water sorption isotherm (adsorption and desorption) properties were examined. The source of α-amylase utilized in this study was a germinated sorghum (Sorghum bicolor L. Moench) extract (GSE). The starch samples were subjected to annealing at temperatures of 40, 50, and 60 °C for durations of either 30 or 60 min prior to the process of gelatinization. A significant increase in the annealing temperature and GSE resulted in a notable enhancement in both the water-holding capacity and the sugar content of the starch. The ordering of starches in terms of their freezable water content is as follows: Chickpea starch (C.P.S) > white beans starch (W.B.S) > wheat starch (W.S) > chickpea starch (C.S) > sweet potato starch (S.P.S). The Guggenheim-Anderson-de Boer (GAB) model was only employed for fitting the data, as the Brunauer-Emmett-Teller (BET) model had a low root mean square error (RMSE). The application of annealing and GSE treatment resulted in a shift of the adsorption and desorption isotherms towards greater levels of moisture content. A strong hysteresis was found in the adsorption and desorption curves, notably within the water activity range of 0.6 to 0.8. The GSE treatment and longer annealing time had an impact on the monolayer water content (mo), as well as the C and K parameters of the GAB model, irrespective of the annealing temperature. These results can be used to evaluate the applicability of starch in the pharmaceutical and food sectors.

Effect of Initial Conformation on the Starch Biopolymer Film Formation Studied by NMR

The formation of a rigid porous biopolymer scaffold from aqueous samples of 1% w/v (suspension) and 5% w/v (gel) corn starch was studied using optical and nuclear magnetic resonance (NMR) techniques. The drying process of these systems was observed using a single-sided NMR scanner by application of the Carr-Purcell-Meiboom-Gill pulse sequence at different layer positions. The echo decays were analyzed and spin-spin relaxation times (T₂) were obtained for each layer. From the depth dependent T₂ relaxation time study, it was found that the molecular mobility of water within the forming porous matrix of these two samples varied notably at different stages of film formation. At an intermediate stage, a gradual decrease in mobility of the emulsion sample towards the air-sample interface was observed, while the gel sample remained homogeneous all along the sample height. At a later stage of drying, heterogeneity in the molecular dynamics was observed in both samples showing low mobility at the bottom part of the sample. A wide-angle X-ray diffraction study confirmed that the structural heterogeneity persisted in the final film obtained from the 5% corn starch aqueous sample, whereas the film obtained from the 1% corn starch in water was structurally homogeneous.

Comparative study of the effect of starches from five different sources on the rheological properties of gluten-free model doughs

We investigated the effect of wheat (WS), corn (CS), tapioca (TS), sweet potato (SS) and potato (PS) starches on the rheological properties of starch-hydroxypropylmethylcellulose (HPMC) model doughs. Significant differences were found among model doughs made with different starches in terms of water absorption, development time, and strength. The PS-HPMC dough presented higher maximum creep compliance, followed successively by SS-, TS-, CS-, and WS-HPMC doughs, and the same order was found for the degree of dependence of G' on frequency sweep, suggesting that the resistance to deformation depends on network structure stability. More water distributed between hydration sites of HPMC and starch surface, leading to more hydrogen bonds and the formation of stable network. In conclusion, the rheological properties of model doughs are largely due to variation in structural and physicochemical properties of different starches, as well as varying interactions between different starches and HPMC.

Retrogradation kinetics of chestnut starches cultivated in three regions of Korea

Retrogradation kinetics of chestnut starches from three different regions of Korea were investigated during storage at 4 °C. The retrogradation properties were determined using four DSC characteristics: glass transition temperature ( T g ' ), ice melting enthalpy (ΔH_i), amylopectin melting enthalpy (∆H_r) and degree of retrogradation (DR). The Gongju (GJ) starch showed the highest gelatinization enthalpy (∆H_g) value, followed by Gwangyang (GY) and Hadong (HD). T g ' of all samples gradually increased with increasing storage time, while ∆H_i decreased as the storage time increased. ∆H_r of all samples significantly increased after 2 days of storage. DR, calculated based on ∆H_g and ∆H_r, showed a similar tendency with ∆H_r. The retrogradation rates of three chestnut starches were analyzed using the Avrami equation, and the time constants (1/k) were obtained. GY, GJ and HD showed the fastest retrogradation rate in T g ' , ∆H_i, and ∆H_r, respectively suggesting that each sample experienced different retrogradation kinetics in different region.

Thermal properties of frozen water in the native and amorphous starches with various hydration degrees

The melting process of frozen water (FW) in various starches (rice, wheat, potato) that have crystal lattices of A- and B-type has been studied by means of differential scanning calorimetry (DSC). The dependences of the melting temperature (Tm) and heat (Qm) of FW on the size of the water clusters forming in starches with various humidity (the so-called size effect) and on conformational changes of starch molecules upon the destruction of native starch crystals (starch amorphization) have been considered. It has been found that in the native starches with low humidity (<35%) the Tm of FW lies below 0 °C and decreases with the decrease of their humidity. The sizes of the water clusters formed under these conditions have been estimated. In contrast, such a size effect in amorphous starches has not been observed and possible reasons for its masking have been discussed. Still, all the values of Tm for FW obtained in the amorphous starches are also negative thereby indicating the dispersed state of water in these systems. Conversely, the size effect for Qm of FW in starches with low humidity, very pronounced in the amorphous state and barely visible in the native one, has been found. It has been established that the starch amorphization leads to a redistribution of the relative amounts of FW and unfrozen water (UFW) resulting in the decrease of Qm for FW in both A- and B- starch types. Finally, it has been concluded that in all the investigated starches there exist water clusters with Tm and Qm lower than that of bulk water.

Anticancer activity of starch/poly[N-(2-hydroxypropyl)methacrylamide]: biomaterial film to treat skin cancer

In the present work, films of pHPMA, pHPMAS hybrid, pHPMA-CPT and pHPMAS-CPT hybrid were prepared by solvent casting method and characterized by FT-IR, FT-Raman, XRD and DSC, respectively. The biocompatibility of the prepared pHPMA film and pHPMAS hybrid film were assessed using VERO cell lines and the percentage cell viability was found to be 97.4 and 98.3% for 7.8 μg/ml of the film extracts after 72 h of incubation. The cancer cell viability of the pHPMA-CPT film and pHPMAS-CPT film using MCF7 cell lines at pH 5.5 and 7.4 were found to be 4.9 and 8.6% and 7.7 and 12.3%, respectively. In vitro release of camptothecin from pHPMA-CPT and pHPMAS-CPT films in phosphate-buffered saline solution at pH 5.5 and 7.4 were monitored and analyzed using UV-vis spectrophotometer at λmax of 360 nm.

Cellulose nanocomposite biopolymer foam--hierarchical structure effects on energy absorption

Starch is an attractive biofoam candidate as replacement of expanded polystyrene (EPS) in packaging materials. The main technical problems with starch foam include its hygroscopic nature, sensitivity of its mechanical properties to moisture content, and much lower energy absorption than EPS. In the present study, a starch-based biofoam is for the first time able to reach comparable mechanical properties (E = 32 MPa, compressive yield strength, 630 kPa) to EPS at 50% relative humidity and similar relative density. The reason is the nanocomposite concept in the form of a cellulose nanofiber network reinforcing the hygroscopic amylopectin starch matrix in the cell wall. The biofoams are prepared by the freezing/freeze-drying technique and subjected to compressive loading. Cell structure is characterized by FE-SEM of cross sections. Mechanical properties are related to cell structure and cell wall nanocomposite composition. Hierarchically structured biofoams are demonstrated to be interesting materials with potential for strongly improved mechanical properties.

Multi-level approach for the analysis of water effects in corn flakes

The purpose of this work was to analyze the effect of water on thermal transitions, mechanical properties, and molecular mobility in corn flakes (CF), and their relationships. Commercial common (CCF) and sugar-frosted (SCF) corn flakes were studied in a water content (wc) range from 5 to 20 (% dry basis). The slope of (1)H NMR spin-spin relaxation time T 2* (determined by FID) versus temperature plot changed close to T g. Compression force showed a maximum at wc of ca. 12 and 16% (db) for SCF and CCF, respectively. (1)H NMR complemented DSC data in determining the temperature dependence of water and solid mobility, in order to assess quality of laminated corn products. The results of the present work indicate that while the compression force showed a maximum value as a function of water content, T g values determined by DSC or by spin-spin relaxation decreased progressively with increasing water content.

Starch gelatinization

Starch occurs as highly organized structures, known as starch granules. Starch has unique thermal properties and functionality that have permitted its wide use in food products and industrial applications. When heated in water, starch undergoes a transition process, during which the granules break down into a mixture of polymers-in-solution, known as gelatinization. The sequence of structural transformations that the starch granule undergoes during this order-to-disorder transition has been extensively researched. None of the published starch gelatinization theories can fully and adequately explain the exact mechanism of sequential structural changes that starch granules undergo during gelatinization. This chapter analyzes several published theories and summarizes our current understanding of the starch gelatinization process.

Processing and Characterization of Porous Structures from Chitosan and Starch for Tissue Engineering Scaffolds

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.